Canonically, Decreased Time Rate is not a leveled trait. Period. As a disadvantage, making it leveled is just begging for abuse.
That said, I could get behind the idea of a special enhancement for Affliction which cost +100% per level and decreased the subject's ability to act as though he were getting hit with "multiple levels" of DTR. Such an enhancement would only allow the victim to act every (1+X) turns, where X is the level of the enhancement. Of course, past nine levels -- allowing the victim to act only once every 10 turns -- it would generally (though not always) be more sensible to just use Temporal Stasis instead.